In continuous ink jet printing, ink is supplied under pressure to a manifold region that distributes the ink to a plurality of orifices, typically arranged in a linear array(s). The ink discharges from the orifices in filaments which break into droplet streams. The approach for printing with these droplet streams is to selectively charge and deflect certain drops from their normal trajectories. Graphic reproduction is accomplished by selectively charging and deflecting drops from the drop streams and depositing at least some of the drops on a print receiving medium while other of the drops strike a drop catcher device. The continuous stream ink jet printing process is described, for example, in U.S. Pat. Nos. 4,255,754; 4,698,123 and 4,751,517, the disclosures of each of which are totally incorporated herein by reference.
Full color graphics printing with such continuous ink jet systems is being developed and practiced by Scitex Digital Printing, Inc., in Dayton, Ohio. One challenge with developing a digital color press is to formulate inks which will run in the digital color press. Existing ink formulations are two-dye inks. Such previous inks which were formulated for 120 and 240 dots per inch (dpi) systems were tried in the digital color press, but unfortunately exhibited severe raggedness after a very short time. Furthermore, the prints produced were poor quality and unacceptable.
One major difference between the digital color press and previous systems is the orifice diameter, which is significantly smaller in the DCP as compared to other systems (e.g., 0.7 mil in the DCP compared to 1.8 mils in the Scitex 5000 printer and 1.3 mils in the Scitex 3600). As the orifice diameter decreases, jet straightness and wetting of the orifices in the peg area become vitally important. The slightest deposit or a non-uniform wetting on the orifice plate may cause excessive raggedness of the jets and results in poor print quality.
It is seen then that there is a need for an ink formulation capable of producing high quality acceptable print, which will run in a digital color press system.